1. Field of the Invention
The present invention relates to an overhead projector (OHP).
2. Description of the Related Art
If a lecturer speaks while using visual effects, such as writing letters on the blackboard or giving an explanation using an OHP, the following advantages are obtained:
making a statement clearly understandable by enumerating key words; PA1 increasing credibility of a statement by presentation of data or the like; and PA1 enabling the lecturer to depict a color and structure by means of a photograph, drawing and the like, which can not be expressed by words.
There are various methods of providing these visual effects.
Methods of providing visual effects are classified into a direct method and an indirect method.
The direct method is such a method that a listener directly looks at supplementary data. For example, there is a method in which a lecturer brings an actual object to demonstrate in front of a listener, or a method in which a lecturer has a listener directly look at an actual object or its model to understand the three-dimensional shape. A method in which a poster is put or actual writing is made on the blackboard etc. is also included in this direct method.
On the other hand, the indirect method is such a method that a listener indirectly look at supplementary data, and includes a projection type in which a listener looks at an image projected on a screen, and a direct view type in which a listener directly looks at an image projected on a display.
The direct view type uses a liquid crystal display, a plasma display, a light emitting diode, or the like. Since a large screen display is very expensive and requires a considerably wide storage space when it is not used, a number of medium-sized displays are often set in the case where a direct view type display device is used in a large lecture place. Alternatively, a direct view type display device is often used in a small lecture meeting.
The projection type uses a liquid crystal projector, a slide projector, or an overhead projector.
The liquid crystal projector is a projection type display device using a transmission type liquid crystal panel, and is a device for projecting an image displayed on the liquid crystal panel on a screen. Projected light emitted from a lamp and having transmitted through the liquid crystal panel is enlarged by an optical system and is projected on the screen.
The projected light means light travelling until an image to be projected on a screen reaches the screen. That is, light in the space from a liquid crystal panel through which the light transmits to a screen which the light reaches, is defined as the projected light.
The liquid crystal projector is designed such that a personal computer can be connected thereto, and an image displayed on a display of the personal computer is directly displayed on a liquid crystal panel in the liquid crystal projector, and the image is projected on a screen.
Thus, anything which can be displayed on a personal computer can be projected on the screen. For example, it is possible to move a mouse (in this case, it also functions as a pointer) and to write letters, and further, it becomes possible to project an animation and to explain by using realistic pictures. In addition, since pictures can be easily enlarged or reduced on a personal computer, it is possible to vigorously put stress on what a lecturer wants to be seen, and also in this point, it effectively functions as a means for assisting a lecture.
When the liquid crystal panel of the liquid crystal projector is made high pixels, vivid pictures can be presented, and further, by adopting digital blur correction or an optical system, a uniform bright high picture quality is realized. As a result, even if a projection distance is extended, a clear image can be obtained. Thus, the liquid crystal projector is effective even for a large meeting place of a scale of several hundred persons.
The liquid crystal projector is designed such that it is compact and can be easily carried, and when it is used in combination with a notebook-sized personal computer, it does not require a wide space and can be used even in a small meeting place of a scale of several persons to ten and several persons.
The slide projector uses a method in which an image taken on a film by a camera is made a slide and the slide is projected on a screen by a lamp similarly to the foregoing liquid crystal projector.
Since an image is projected on a screen by the same function as enlargement of a photograph, a clear image with high resolution can be projected. Moreover, since the slide projector uses a powerful lamp, a projection distance is long. Thus, it can be used for a large meeting place of a scale of one thousand persons. Moreover, if the slide projector is set in advance, different images can be sequentially supplied by only a switching operation.
The overhead projector (OHP) is a device in which letters or figures are written by an oily pen or are printed on an OHP film made of transparent resin to prepare data for projection, and the data are projected on a screen by a lamp.
The OHP has a feature that although projection is made on an almost vertical screen, an OHP film is placed horizontally. Thus, it is necessary to change the travelling direction of projected light. A mirror is used as a means for changing the travelling direction of projected light. By causing the projected light to be reflected to change its travelling direction, it is possible to project an image on an almost vertical screen.
In the case of a transmission type OHP, as shown in FIG. 6, projected light emitted from a lamp 601 and having transmitted through an OHP film 105 is enlarged by an optical system 108 set above the OHP film, is reflected by a mirror 602 set above the optical system, and is projected on a screen 106.
The optical system is constituted by one or plural lenses, and serves to enlarge or reduce an image, and to adjust focus.
In the foregoing device, although the enlargement of projected light is made prior to the reflection by the mirror, there is also a device for making enlargement after reflection by a mirror. Further, there is also a device in which optical systems are set before and behind a mirror.
There is a plane lens 603 under a stage 104 on which a transparent film is put. Light is emitted from the lamp 601 set below the plane lens, is refracted by the plane lens, and transmits through the transparent film 105 to become projected light. Since this projected light is refracted by the plane lens, it is designed such that the projected light goes in the optical system 108 smaller area than the transparent film.
Focusing can be made through a distance 604 between the plane lens 603 and the optical system 108, or through a distance 605 between the optical system 108 and the screen 106. Concretely, focusing is made by moving the optical system 108 or moving a head portion 107 of the OHP.
Since the structure of the OHP is simple, it has the following advantages: it is inexpensive; it can be compactly folded so that it is convenient to carry; preparation of data is easy; and there is little trouble during a lecture. Accordingly, the OHP is naturally used in a workplace or a meeting place, and is also often used among students. That is, the OHP is a most popular display device for a lecture at present.
There are mainly methods (1) to (3) described below as methods of recording the content of a lecture.
(1) Documents such as a paper and drawing
A method in which one looks at documents such as a copy of supplemental data for an OHP or the like used in the lecture, a paper describing the content of the lecture summarized in shorthand, and an outline of the content of the lecture summarized by a lecturer himself or herself.
(2) Voice
A method in which the content spoken by a lecturer in the lecture is recorded by a tape recorder or an MD disc, and is later reproduced to be heard.
(3) Picture
A method in which pictures are recorded by a video camera, and both voices and pictures are reproduced later. The video camera includes an optical system, an image pickup portion, and a recording portion, and it is possible to take an image at the same viewpoint as a listener. Thus, in the case of a lecture where a projection type display device such as an OHP is used, the object of the image pickup is mainly a screen and a lecturer.
However, the above-mentioned methods have problems to be solved by the present invention, as described below.
In the case of only the method (2) (voice)
In a lecture, understanding of the content is often promoted by addition of visual effects, such as writing letters on a blackboard or giving an explanation using an OHP. Thus, there is also a case where it is insufficient to use only the method (2).
In the case of only the method (1) (documents such as a paper and drawing)
In the method (1), it is impossible to hear to the voice of a lecturer. Also, since it is impossible to transmit the atmosphere at the meeting place by only the documents, there is also a case where only reading of the documents summarized in shorthand is insufficient as a method of completely knowing the content.
In the sense of adding visual effects, it appears that a copy of supplemental data for an OHP or the like and writing on the blackboard are sufficient. However, since these data are absolutely used for supplementing the content of the lecture, it is meaningless to attach only the data. These supplemental data can become meaningful data in such a case that the relation between the content of the lecture and these data is sufficiently explained.
Since an outline summarized by a lecturer himself or herself includes an assertion of the lecturer as well, and is often explained by use of drawings, it is a most frequently used method.
However, such an outline is usually prepared prior to the lecture. As a result, there is a case where new facts are known or new consideration is made after the preparation of the outline, so that there is a case where a part of the content of the lecture is not set forth in the outline, and sometimes, there is a case where an important portion of issues is not set forth in the outline. Moreover, an episode such as a talk about failure, which is not so worth writing in the outline, can be experienced by only a listener of the lecture.
In the case of combination of the methods (1) and (2)
This is a method in which while a copy of supplemental data for an OHP or the like is seen or a document written on the content of a lecture is seen, a recorded talk of a lecturer is heard. Since the voice of the lecturer can be heard as compared with the case of only documents, what is emphasized by the lecturer is understood. Moreover, since visual effects are also added, this method is superior to only the method (1) or method (2).
However, since the position of a pointer is not recognized while the lecturer speaks, a place to be seen in the supplemental data can not be recognized, and further, since the gesture of the lecturer can not be seen, there is a case that this method is insufficient as a method of completely understanding the content of the lecture.
As described above, according to only the method (1) of document or method (2) of voice, it is impossible to make record to the extent of the content indicated on an OHP film or a projection screen by a lecturer using an indicting stick or a laser pointer.
In the case of method (3) (picture)
As compared with other methods, this method is preferable as a method of recording all the content of the lecture since both the picture and voice can be recorded. Although a recording device and a recording tape are expensive, and the device requires a setting place so that it sometimes becomes an obstacle to the audience, since it is possible to understand the content of the lecture accurately, quickly and easily, this method is extremely excellent as a method of recording the content of the lecture.